The present invention relates generally to microwave components, and more specifically, to tunable microwave components constructed using composite dielectrics.
Conventional microwave components are typically designed by establishing specific values of the characteristic impedance and the electrical length of transmission line segments within a particular component. Maintaining specific characteristic impedances and electrical lengths is desirable so that a circuit or system can operate within particular design parameters. As a result, circuits are typically designed relative to these values such that a circuit or system can achieve desired performance. To establish specific values of characteristic impedance and electrical length, typical tunable microwave components are often constructed utilizing materials having fixed electric permittivity and magnetic permeability, as permittivity and permeability contribute to the calculation of such values.
As will be appreciated by those of skill in the art, tunable microwave devices have also been fabricated using either tunable magnetic or ferroelectric components. However, using only magnetic or electrical tuning components can result in an impedance mismatch because the characteristic impedance of a transmission line is directly proportional to the square root of the ratio of magnetic permeability to electric permittivity. The mismatch will become apparent when a device that incorporates only magnetic or electrical tuning components, such as a tunable microwave filter, is attempted to be tuned. This impedance mismatch can cause transmission problems and reduced component performance, and reduced performance of the system in which the device is included. Furthermore, the use of other tunable materials, such as ferrite rods, FETs, PIN diodes and varactor diodes (also called veracitors) in constructing frequency agile systems has often lead to undesirable high microwave losses. Many of these devices, while performing their tuning function, highly attenuate the microwave signals or cause excessive radiation of the microwave signals. Additionally, many of the currently used tunable devices cause intermodulation distortion (IMD) when information is modulated onto the microwave carrier signal.
Low-loss, high speed, tunable microwave components are useful in a variety of electrical systems, and may be necessary for the construction of certain systems, such as next generation communication systems. For example, next generation systems require that microwave losses be minimized to achieve suitable signal to noise ratios, and that microwave devices enable switching speeds that are increased over current speeds by one or two orders of magnitude. This is clearly evident in applications involving barium strontium titanate (BST) thin films, which are deposited by pulsed laser deposition (PLD) onto dielectric substrates and are currently being used to develop frequency agile microwave electronics. Nevertheless, the characteristic impedance of these devices suffers a large change when the dielectric constant is reduced by a large factor, such as a factor of four or more. This reduction in the dielectric constant could occur, for example, during the process of tuning the filter.
Therefore, in order to construct next generation systems, high performance, efficient, frequency agile microwave components are needed that have relatively low microwave losses, constant impedance, and high switching speeds, for use in higher speed electronic systems.
The present invention discloses tunable microwave components including a strip line or microstrip transmission line having a composite dielectric constructed with both ferroelectric (FE) and ferromagnetic (FM) materials. The FE and FM properties of these respective materials can be varied with externally applied electric and magnetic fields such that the electrical length (or phase length) of the transmission line can be varied without varying the characteristic impedance of the transmission line. Thus, the component can be electrically tuned to operate at different frequencies without adversely affecting the impedance matching of the circuitry. As a result, a microwave component according to the present invention can be used in a variety of microwave devices, such as phase shifters, frequency filters, directional couplers, power dividers and combiners, impedance matching networks, and the like.
According to one embodiment of the present invention, there is disclosed a tunable low-loss microwave component, in communication with a power source producing an applied voltage and an applied current. The tunable component includes at least one ferroelectric (FE) material, wherein the at least one FE material changes electric permittivity with the applied voltage, and at least one ferromagnetic (FM) material, wherein the at least one FM material changes magnetic permeability with the applied current, such that the tunable microwave component is tunable to at least a first frequency when the component is a non-bias state, and tunable to at least a second frequency when the component is in a bias state, and wherein the tunable microwave component has a constant characteristic impedance at the first and second frequencies.
According to one aspect of the present invention, the tunable microwave component has a constant electrical length at the first and second frequencies. According to another aspect of the present invention, the at least one FE material and the at least one FM material can be mixed to create a FE/FM composition having both FE and FM material properties. Furthermore, the FE material can include barium strontium titanate. Additionally, according to the invention, the tunable component can include a first conductor in communication with the power source, wherein voltage and current applied via the first conductor can cause the tunable microwave component to enter the bias state. Moreover, the tunable microwave component can be a microwave transmission line.
According to one embodiment of the present invention, there is disclosed a microwave transmission line. The microwave transmission line includes a first conductor, a second conductor, and a central conductor disposed between the first conductor and the second conductor. The microwave transmission line also includes a composite, comprising at least one ferroelectric material and at least one ferromagnetic material, wherein the composite substantially surrounds the center conductor, such that the transmission line is tunable to at least a first frequency when the composite is a non-bias state, and tunable to at least a second frequency when the composite is in a bias state, and wherein the microwave transmission line has a constant characteristic impedance at the first and second frequencies.
According to one aspect of the present invention, the composite can include a mixture of the at least one ferroelectric material and the at least one ferromagnetic material. According to another aspect of the invention, the composite can include one block of the at least one ferroelectric material and one block of the at least one ferromagnetic material, and wherein the block of the at least one ferroelectric material is located adjacent the center conductor and adjacent to the first conductor, and wherein the block of the at least one ferromagnetic material is located adjacent the center conductor and adjacent to the second conductor. According to yet another aspect of the invention, the composite can include alternating layers of the at least one ferroelectric material and the at least one ferromagnetic material.
According to another embodiment of the invention, there is disclosed a method of creating a tunable, low-loss transmission line having outer conductors and a central conductor. The method includes providing at least one ferromagnetic (FM) material, providing at least one ferroelectric (FE) material, combining the at least one FM material and the at least one FE material to produce a FM/FE composition, surrounding the center conductor with the FM/FE composition, and sandwiching the FM/FE composite and center conductor in between the outer conductors.
According to one aspect of the present invention, combining the at least one FM material and the at least one FE material includes mixing the at least one FM material and the at least one FE material to produce a mixed FM/FE composition. Furthermore, combining the at least one FM material and the at least one FE material can include alternating layers of the at least one FE material and the at least one FM material to produce a layered FM/FE composite. According to yet another aspect of the present invention, combining the at least one FM material and the at least one FE material includes locating a block of the at least one FE material adjacent the center conductor and adjacent one of the outer conductors, and locating a block of the at least one FM material adjacent the center conductor and adjacent one of the other outer conductors.
According to yet another embodiment of the invention, there is disclosed a method of constructing a microstrip circuit. The method includes providing a thick film FM/FE composite, including at least one FM material and at least one FE material, disposing microstrip transmission lines on the thick film FM/FE composite, locating the thick film FM/FE composite directly adjacent a microwave substrate, and providing a ground plane located adjacent the microwave substrate on a side of the microwave substrate located opposite the thick film FM/FE composite.